DEVELOPMENT AND DEPTH DISTRIBUTION OF THE EGGS OF ORANGE ROUGHY, HOPLOSTETHUS-ATLANTICUS (PISCES, TRACHICHTHYIDAE)

The development of the eggs of deep-sea fish has seldom been described . The eggs of orange roughy (Hoplostethus atlanticus), a mid-slope ben thopelagic fish, were fertilized and incubated at three temperatures. Those incubated at 7 degrees C hatched at 13 days; wild eggs were esti mated to hatch at 7.3 days. Their development rate was similar to that of eggs of fish from other orders and of shallower-living species. Fr om depth-stratified plankton samples, early-stage eggs were found at 5 00-700 m. Their buoyancy was estimated to be 6.02 kg m(-3), the upper end of the range of known fish-egg buoyancies. The eggs rose to the up per mixed layer at an estimated 23.8 m h(-1), which is faster than asc ent rates reported for other fishes. Their relative buoyancy and large size would be the reason for this faster rate. However, large egg siz e is apparently not an adaptation to enhance development rate; the mor e rapid rise into warmer water reduces development time but does not f ully compensate for the slower development.